I realized the other night that as I speak with people of different cultures, my "proper" English actually gets worse. I sometimes catch myself using "broken English" things like "they think I'm bad player" *shudder*

On the other hand, as long as you don't sound like a complete jackass or type like the l33t kidz, there's no reason to get up in arms about these things. The "could of" thing drives me nuts too, but I understand that they are trying to say "could have". You will invariably slip up as you have done in this same post, and get called out on it (and apparently not be able to take the criticism)...